I am a grad student in Bioengineering working on a sterlization project.
The method that I use for judging the extent of sterlization is the Plate
Count method. Since I have NO undergrad background in Micro, I am
struggling. I have a few questions to ask, so please bear with me.

Q1) After one experiment I found 2 types of colonies growing on the plate.
One was distinct E. Coli like ( round and whitish) The other was like
smudge, but with distinct colonies. So I used EMB agar to test them and to
my surprise, The smudge colonies gave a green sheen and the E. COli looking
colonies did not. How is that possible?

Q2) Another weird thing is that I had streaked an EMB late from an isolated
E. COli colony a few days ago and the plate did show Green sheen but after I
taped it and kept it in the fridge for a few days, the sheen disappeared. Is
that supposed to happen.

Q3) My lab is looking at different methods to judge the degree and the
mechanism of Sterlization i.e. microbial killing. Can anyone suggest
something other than Plate Count.

Sounds to me like it is critical that your microbiological data is not only
comprehensive but accrurate for this project.

As you state you are not a microbiologist and with respect it does show.
For example you notes include no mention of measurment of anaerobes which
of course would not show up by aerobic plate count nor any accomodation for
fungi.

Additonally the sensitivity of the plate count technique is insufficient to
really measure efficiency in processes where actual sterility is the goal.
More sense is obtained by liquid culture of large masses inorder to
detrmine the presence of low numbers of survivors.

My recommendation is you either hire a microbiologist or call in the
temporary services whose skill base and resources are sufficient for the
job at hand.

You seem to be at a university. Go talk with some microbiologists
there. Microbiological technique is not trivial -- and certainly not
easy to describe in short messages. Many (though certainly not all)
people enjoy working with people in other fields, so you may well
strike up some good collaboration.

Sterilization is a complex issue, with many concerns depending on
context. Offhand, it seems odd that you are using E coli for measuring
sterilization -- though perhaps it is a convenient starting place. It
also sounds like you may be running into some contamination -- not
surprising if you are new to this and using a lab not intended for
such work.

Nachiket Vaze wrote:
Dear Nachi E.Coli wont be a good indicator for sterilization
testing,since many g+ve spore forming bact. are presant in air.you
might be know one fact is that only 1% of bacteria are culturable in
normal way.colony characters are not used to identify the bact. it is
presumbly understandable.many advance chromatography/ spectroscopy
tech. available to identify the presence of organism on/in objects.